دانلود رایگان مقاله انگلیسی تعیین مقاومت بتن مسلح به وسیله مقاومت ظاهری بسته به شرایط پخت - الزویر 2018

ABSTRACT

In this study, change of the electrical resistivity values was investigated on reinforced and unreinforced concrete samples that were designed in different strength of the dry and water saturated conditions. For this purpose, studies were conducted with 150x150x150 mm cubic samples of 9 different concrete designs. A piece of 10, 14 or 20 mm diameter reinforcement was placed in the middle of concrete samples and 18 samples were prepared for all types of them and 9 samples for the unreinforced samples. Some of the prepared these samples were subjected to the water cure and the other part of the samples were kept in the air cure. The potential difference measurements were made by electrical resistivity method on different surfaces of the sample at specific time periods of during the 90 days and apparent resistivity values of the samples were determined. Furthermore, the concrete strength was determined from average of 3 samples by uniaxial compressive strength test of each sample on 7th, 28th and 90th days. Changes of the apparent resistivity and concrete strength values that obtained from these conducted studies were investigated to depending on time. At the same time, the relationship between uniaxial compressive strength and the apparent resistivity was revealed in case of the samples’ being in water or air cure. Accordingly, it was stated that the different curing conditions have an effect on the apparent resistivity of concrete and concrete strength. Therefore, while the apparent resistivity of the concrete design having different strengths increased depending on increasing concrete compressive strength of samples in the water cure; it reduced in the air cure. This research is important in terms of both time and being economical by providing a non-destructive approach to the determination in-situ of the concrete strength of the water or gas saturated old and new concrete structures.

5. CONCLUSION and DISCUSSION

In the result of the fracturing with uniaxial compressive strength test of reinforcement concretes that are performed water or air cure; while the reinforcement concrete strength value increases as reinforcement diameter increases in loose strength concretes, high strength concretes decrease as reinforcement diameter increases. According to the work done in general, the increase in the electrical resistivity of the concrete also increases the compressive strength, taking into account only the samples in the water environment (Chen et al., 2014). However, curing conditions have an important effect on the electrical resistivity (Ferreira and Jalali, 2006; Simon and Vass, 2012). Especially when the existing structures are assessed in situ, whether they are moist or dry will change the measurement results. For this reason, researchers such as Polder (2009) do not recommend using the electrical resistivity method in evaluating the concrete pressure resistance. However, the change in resistivity due to curing conditions can be clearly demonstrated in this study.

While determining the electrical resistivity of concrete designs having different strengths and curing conditions, the resistivity increased due to the increase in the compressive strength of concrete samples in the water cure; it reduces in the air cure. When compared to samples of the same design, resistivity values decreased with water saturation, as long as the sample dried and air fills in the pores depending on time, accordingly this, resistivity values also increased.